Image: “A seesaw or teeter-totter in a children’s playground in Ottawa, Ontario, 2010.” By Photo by M. Rehemtulla. License: CC BY 2.0

Definition of Torque and Equilibrium

The definition of equilibrium is found in the word itself. It deals with equal parts implying a balance. If an object has forces acting on it, the object may undergo motion. However, if the object is in equilibrium, then the object will not move since all the forces balance each other.

One way to look at the motion of an object is to separate the forces acting on the object into horizontal and vertical forces. In equilibrium, the horizontal forces will balance themselves and the vertical forces will balance themselves. Thus, no motion of the object will occur in either the horizontal or vertical axes.

Torque causes an object to rotate about an axis. It depends on the distance between the axis and the point where the force acts. Force multiplied by force arm equals load multiplied by load arm. Torque can be described in the following equation:

M = r * F

M ⇒ Torque [N * m]

Example: Muscles work on joints, which from a physical pivot point with their axes. When force is exerted upon them, they create a torque.

τ = r * F

τ = r * F sin(Θ)

[τ] = N * m

Parallel: τ = 0
Since sin 0 = 0
and sin 180 = 0

τ = r * F sin(Θ)

[τ] = N * m

Parallel: τ = 0

Perpendicular: τ = r * F

τ = r * F sin(Θ)

[τ] = N * m

Parallel: τ = 0

Perpendicular: τ = r * F

τ = F (r sin(Θ))
τ = F * I

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